This invention relates to recording systems and more particularly to a recording system for recording transduced electrical signals on a recording medium with a recording apparatus having a mode of operation responsive to the transduced electrical signals. Even more specifically, this invention is directed to systems for recording dictation. With respect to such a recording system, it is known in the art to use a detection and control apparatus for initiating and terminating the recording mode of operation of a recording apparatus in response to the presence or absence of sound generated electrical signals so that the recording apparatus is in the recording mode of operation only when there is dictation to be recorded.
The detection and control apparatus starts the recording mode of operation of the recording apparatus in response to sound generated electrical signals and terminates the recording mode of operation of the recording apparatus in response to the absence of sound generated electrical signals for a predetermined length of time. A detection and control apparatus is particularly useful in a recording system in which the source of the sound to be recorded is an individual who wishes to record dictation and who is remote from the recording apparatus with no means for controlling the recording mode of operation of the recording apparatus other than the sound of his voice and resulting sound generated electrical signals.
A difficulty which has been encountered in the use of a detection and control apparatus in a recording system is that the recording apparatus is not instantaneously placed in a recording mode of operation upon the initial detection of sound generated electrical signals by the detection and control apparatus. Therefore, the recording apparatus is not operating in the recording mode of operation when sound, such as the voice of a dictator, initially reaches the recording apparatus to be recorded as sound generated electrical signals. Thus, some of the sound, such as dictation, to be recorded is lost.
In order to solve this problem some prior art recording systems have used a supplementary recording device as a stage in the transmission of the sound generated electrical signals to the recording apparatus. This supplementary recording device records the initial sound and all subsequent sound as sound generated electrical signals and plays the sound generated signals back after a time delay to the recording apparatus for recording by the recording apparatus. The length of this time delay is determined by the length of time needed for the recording apparatus to be placed in the recording mode of operation by the detection and control apparatus after detection of the initial sound generated electrical signals by the detection and control apparatus. Once placed in the recording mode of operation by the detection and control apparatus, the recording apparatus receives and records the delayed initial sound generated electrical signals and all subsequent signals from the supplementary recording device until sound generated electrical signals have ceased for a predetermined length of time to cause the detection and control apparatus to terminate the recording mode of operation of the recording apparatus.
A recording system having a continuous loop recording device as a supplementary recording device is an example of a prior art recording system which uses a supplementary recording device. The continuous loop recording device has a recording head and a playback head positioned along a continuous loop of a recording medium, such as tape. The distance between the heads is such that the period of time required for the transit of the tape from the recording head to the playback head provides the time delay required for a detection and control apparatus to place the recording apparatus in the recording mode of operation.
The disadvantages of this and other prior art recording systems using supplementary recording devices are in the inherent risk of a mechanical failure or of tape breakage in the supplementary recording device. Moreover, the duplication of recording required the duplication of costly components in the supplementary recording device and in the recording apparatus and additional space to accommodate both the supplementary recording device and the recording apparatus. Furthermore, gradual degradation of the signal in the process of recording, playing back, and re-recording sound generated electrical signals introduces a substantial amount of distortion into the final desired recording of sound by a recording apparatus and thereby diminishes the quality of the recording.
In an effort to solve some of the problems encountered with prior art recording systems using supplementary recording devices, the prior art has also used an analog shift register in a recording system for delaying sound generated electrical signals in their transmission to a recording apparatus. While this recording system avoids some of the problems of cost and size encountered with prior art recording systems using supplementary recording devices, as well as the problems of tape breakage or mechanical failure, this prior art recording system still causes a gradual degradation of the sound generated electrical signals to be recorded by a recording apparatus and thereby diminishes the quality of the recording.
This diminution in the quality of the recording is unavoidable because the sound generated electrical signals are analog signals and because distortion of an analog signal usually occurs when an analog signal is amplified and processed through an analog shift register to provide a time delay. Moreover, the infinite variety of distinct analog wave forms in an analog signal generated by sound such as human speech precludes any reconstruction of the analog signal after it has been passed through the shift register.
Therefore, the quality of the recording is irretrievably lost after distortion in an analog shift register. The invention disclosed herein solves this problem of distortion by gradual signal degradation and other problems encountered in prior art recording systems having a detection and control apparatus to control the recording mode of operation of a recording apparatus so that the recording apparatus is in the recording mode of operation when there is sound to be recorded.